We present an equilibrium theory for strain relaxation in epitaxial layers grown on substrates of a finite dimension. The conventional dislocation model is refined to take account of the multiple reflection of image dislocations. The effect of strain transfer and dilution due to finite vertical and lateral dimensions of the substrate is also considered. The critical thickness has been obtained based on an energy balance approach. Detailed numerical analysis with primary experiments for the SiGe alloy system is also provided.

The authors use a lateral emitter resistor in floating base GaAs/InGaAs/AIGaAs heterojunction bipolar photo-transistors to reduce the surface recombination in the vertical wall of the emitte-base junction and increase the photo-sensitivity at low injection levels. The same process also reduces the dark current in the reverse biased collector junc-tion.

The authors report regenerative switching in an npn Si/Si0.7Ge0.3/Si heterojunction bipolar transistor with a δ-doped base is reported. When operated in the avalanche regime the device exhibits switching characteristics in collector current against emitter-collector bias voltage. The I-V curve also shows multisteps between the OFF and ON states at room temperature, which may be due to the quantised energy levels formed by the thin δ-doped base

Epitaxial lift-off (ELO) techniques were employed in the fabrication of lnP/InGaAs vertical surface light emitting diodes and resonant cavity enhanced photodetectors on Si. External mirrors were employed consisting of Si/SiO2 quarter wave dielectric stacks. The main peak in the emission spectrum of the fabricated device has an FWHM of 8nm. The spectral response of the photodetector shows wavelength selectivity, and with an lnGaAs absorbing layer only 0.1μm thick a peak quantum efficiency of 0.48 was obtained in the 1.5μm spectral region.

A Si-based waveguide photodetector with a response in the 1.3-1.55-m wavelength range is demonstrated. The active absorption layer of the pin photodiode consists of a SiGeC alloy epitaxially grown on a Si substrate with a Ge content of 55% and a thickness of 800 A℃. The external quantum efficiency for a 400-m-long waveguide, measured by using a single-mode fiber coupled to the waveguide facet, is 0.2% at 1.55m. The dark current density at peak photoresponse is 40pA/m2. The quantum efficiency can be further enhanced by using multiple SiGeC layers as the absorber. Direct measurements of the absorption coefficient for the alloy layer are also reported.